Light transmission through a subwavelength slit: Waveguiding and optical vortices

Abstract

The anomalous ͑i.e., more than 100%) light transmission through a subwavelength slit in a thin metal plate is accompanied by a combination of waveguiding and phase singularities of the field of power flow near the slit. The crucial role of these phase singularities ͑such as optical vortices and saddle points͒ in exciting the waveguide modes is systematically studied. We predict transmission efficiencies as high as 300% for certain configurations. DOI: 10.1103/PhysRevE.67.036608 PACS number͑s͒: 42.25.Bs, 42.25.Fx The analysis of light transmission through a slit with a subwavelength width in a thin plate is a subject with a venerable history ͓1-3͔, dating back to Lord Rayleigh. Because of its importance for near-field optics and semiconductor technology, it continues to attract attention. Recently Ebbesen et al. observed extraordinary light transmission ͑i.e., more than 100%) through an array of subwavelength holes ͓4,5͔, which led to a new wave of interest in the subject. Broadly speaking there are two mechanisms involved in extraordinary light transmission: the coupling of light with surface plasmons ͓4 -8͔, and Fabry-Pérot-like resonances inside the apertures ͓9-11͔.In this paper we study the light transmission for a different configuration, namely, a single subwavelength slit in a metal plate of finite conductivity for the TE-polarization case ͑i.e., with the electric field parallel to the slit͒. TE polarization differs from TM polarization in that no surface plasmons are excited ͓12͔. Furthermore, for TE polarization the first waveguide mode in a perfect conductor has a cutoff width of w cut-off ϭ/2, with being the wavelength. However, due to their finite conductivity, efficient energy transport may be possible at smaller slit widths in realistic metal plates. A rigorous computation of the field demonstrates that near these cutoff widths, there is an enhanced transmission through the slit. Transmission efficiencies as high as 300% are found for special configurations. We emphasize that these remarkable enhancement effects occur even though there is no coupling to surface plasmons.To elucidate why the field couples so effectively with the propagating waveguide modes, we have analyzed the field of power flow ͑i.e., the time-averaged Poynting vector͒ near the slit. It is found that this field exhibits optical vortices and other kinds of phase singularities ͓13-15͔, which are arranged in an arraylike pattern. We find that the location and annihilation or creation of these phase singularities are intimately connected with the phenomenon of enhanced transmission.The field around a single, infinitely long, slit in a metal plate was calculated using a rigorous scattering approach ͓16͔. The total electric field E is written as the sum of two parts, namely the incident field E (inc) and the scattered field E (sca) . The incident field is the field that would occur in the absence of the slit in the plate. The illuminating field is taken to be monochromatic and propagating perpendicular to the plate. We have suppre...

Transmission properties of a single metallic slit: From the subwavelength regime to the geometrical-optics limit

“…Due to the translational invariance of the system along the y axis, it is possible to write the vectorial Maxwell equations as two decoupled differential equations, one of them corresponding to s-polarization (electric field, E, parallel to y axis) and another corresponding to p-polarization (magnetic field, H, parallel to y axis). The case of spolarization has been throughly analyzed in [17]. Here, we concentrate on p-polarized light in which resonant transmission properties have been reported.…”

Dynamic Beam Steering from a Subwavelength Slit by Selective Excitation of Guided Modes

“…This so-called extraordinary optical transmission has been attributed to the coupling of light with surface plasmon polaritons [5][6][7] and to Fabry-Pérot cavitylike resonant modes [8,9]. Different optical phenomena, like beaming [10] and wave guiding [11], have been predicted and observed in these systems.…”

Connection between Phase Singularities and the Radiation Pattern of a Slit in a Metal Plate

“…In the configuration of Fig. 1, the second symmetric mode is propagating for a slit width w > 1:4 for TE-polarized fields or w > 0:9 for TMpolarized fields [3]. (No antisymmetric modes are excited because the illuminating field is symmetric.)…”

“…This method, commonly referred to as the Green's tensor method, is described in detail in [6], and has been applied previously by us to study similar configurations [3][4][5].…”

“…In previous articles [3][4][5], a connection was made between the transmission coefficient of a subwavelength slit and phase singularities of the time-averaged Poynting vector field on the illuminated side of the metal plate. We now show that the phase singularities of the electric or magnetic field on the ''dark'' side of the metal plate are intimately connected with the radiation properties of the slit.…”